Titanium alloys



United States Patent 3,199,980 TITANIUM ALLOYS Harold Brooks,Farnborongh, Anthony Reginald George Brown, Farnham, Kenneth Stanley.Iepson, Ash Vale, and Gerald Ivor Lewis, Farnborough, England,assignors to National Research Development Corporation, London, EnglandNo Drawing. Filed Aug. 29, 1062, Ser. No. 220,157 Claims priority,application Great Britain, Sept. 4, 1961, 31,678/61 3 Claims. (Cl.75-1755) This invention relates to titanium base alloys and is moreparticularly directed to solving the difiiculty experienced in usingmany titanium alloys for structural purposes owing to the relatively lowmodulus of elasticity of these alloys.

It is known that alloys of titanium and aluminum show increased modulusand strength as the aluminum content is increased until at about 8%aluminum they become brittle. This addition of aluminum does not,however, improve properties of the alloy to the desired level. Furtherit has been shown that the addition of a dispersed phase of high modulusand strength alloying elements such as carbon and boron to a titaniumbase alloy may improve the strength and modulus of elasticity of theoriginal material.

According to the present invention a series of alloys having atitanium-aluminum a solid solution matrix containing from 1% to 7% byweight of aluminum is strengthened and has its Youngs modulus raised bythe simultaneous addition of boron not exceeding 200% by weight andcarbon not exceeding 1.2% by Weight, the said additions beingprecipitated from the melt on cooling and forming a dispersed phasewithin the oc solid solution matrix.

In a preferred composition the limits of the proportions by weight ofthe alloying elements are aluminum 3 to 7%, boron 0.5 to 2.0% and carbon0.1 to 1.2%.

It should be noted that below 3% aluminum the strengthening effect ofthe aluminum on the Ti-Al solid solution is not significant, and above7% aluminum the alloys containing boron and carbon become unworkable.

Similarly below 0.5% boron the effect on Youngs modulus and strength isnot significant. Above 2.0% boron the formation of primary boride in thealloys results in undesirable-properties.

The limits of carbon content are set for similar reasons.

Generally, alloys according to the invention may be prepared by any ofthe normal processes used for the production of titanium alloys, suchas, for instance,

(a) Powder metallurgy techniques (b) Non-consumable arc melting underinert gas and (c) Vacuum consumable arc melting.

Experimentally the raw materials consisting of titanium (sponge orpowder), aluminum (foil or wire), graphite powder, and boron or titaniumdiboride powder are mixed in the required proportions. In thenon-consumable arc melting process small cylinders of the compactedmixture are pre-melted under inert gas to buttons of alloy, the buttonsbeing subsequently remelted in a larger furnace to build an ingot. Inthe consumable arc melting process the components are pressed into theform of an electrode (or if a large enough press is not available intosections of an electrode which are subsequently welded togther). Thiselectrode is then melted in a consumable electrode vacuum arc furnace toproduce an alloy ingot.

The ingots are then forged in the normal way and subsequently rolled tobar, or clad with commercially pure titanium sheet and rolled to sheetas described in British Patent No. 822,750.

3,199,980 Patented Aug. 10, 1965 Several examples of the invention willnow be described.

Example 1 36 compacts each of 10 gram weight and containingTi+5%Al-|-1.5%B+0.3% C. (by weight) were made up from titanium sponge,aluminum foil, powdered crystalline boron, and powdered graphite. Thealuminum foil was formed into a small envelope and the boron and carbonpowders were enclosed in this envelope which was then pressed into thecentre of the alloy compact. The compacts were melted into buttons in atungsten electrode non-consumable arc furnace under a pressure of 20cms. Hg of argon. 'Melting was for 2 mins. at 300 amps. The buttons werethen turned over and remelted under the same conditions.

These buttons were then melted into a 360 gram ingot about 2 /2"diameter in a second tungsten electrode nonconsumable arc furnace, undera pressure of 20 cms. Hg of argon at 400-750 amps. V

The ingot was removed, heated to 1100-l120 C. in a muffle furnace andhammer forged to /2" x /2" section bar.

The bar was annealed for 4 hrs. at 850 C. in vacuo (pressure-approx. 10mm. Hg) 'and then machined into test pieces for tensile tests,determination of dynamic Youngs modulus, and Izod impact strength. Thecomposition and results of tests at room temperature were as follows.

Nominal Composition 5% Al, l.5% B, 0.3% C. Actual Composition 4.85% Al,1.45% B, 0.28% C.

' 0.1% proof stress tons/sq. in 66.7 U.T.S. tons/sq. in 77.2 Elongationpercent 13.0 Estm; P.S.l 212x10 Enymmic p.s.i 20.9 10

Impact strength ft. lb 3 Example 2 A second ingot was produced using thesame method as described in Example 1.

The ingot was heated to 1120 C. and hammer forged to a slabapproximately 1" thick. This slab was machined on its major surfaces,and clad with 0.060" thick commercially pure titanium sheet. It was thenhot rolled to 0.064 thick sheet, using approximately 10% reduction perpass and rolling at 1080 C.

The sheet was grit blasted and pickled in an aqueous solution of HF andHNO Blank specimens for tensile testing, and dynamic Youngs modulusdetermination were guillotined from the sheet. The blanks were annealedin vacuo (10 mm. Hg) for 4 hrs. at 850 C. and furnace cooled, and thenfinally machined. The composition and properties obtained were asfollows:

Nominal Composition: 5% A1, 1.5% B, 0.3% C.

Room 400C. Temp.

0.1% Proof stress, tons/sq. in 61. O 29.1 U.T.S., tons/ sq. in 72 44.3Elongation, percent 5 5 E t m, p.s.i 19. 5X10 15. 7X10 D namic, p.s.i20. 1X10 Example 3 non-consumable arc vacuum furnace to produce aningot. The ingot was hammer forged to a fiat slab, and machined on itsmajor faces. These faces were clad with ,pure titanium. sheet, priortorolling to sheet (in accordance with British Patent No. 822,750). Theforging temperature was about 1100" C. and the rolling temperature 1050"C.

The 0.060""thick'sheet produced by the rolling was machined into testpieces, and the results of tests gave the following properties.

Room 400 0. Temp.

0.1% Proof stress, tons/infl. 61 29 Ultimate Tensile strength, tons/i 7244. 3 Elongation, percent 5 Youngs modulus, p.s.1. 19. 5 15. 7

I I Example4 Sheet material prepared as in Example 3 to the nominalcompositions listed gave the properties indicated in the table below.

Composition (by An alloy prepared as in Example 3 was forgeilat 1 100"C. and then rolled at 1050 C. into barform. The mechanical propertiesdetermined on the bar were. as given below. The nominal composition ofthe alloy was 5% Al,

1.5% B, 0.3% C by weight, balance titanium.

0.1% proof stress, tons/in. 66.7 Ultimate tensile strength, tons/in.77.2 Elongation, percent 13.0

Youngs modulus, p.s.i. 21.2

4 Example" 6 An ingot of nominal composition by weight 5% Al, 1.5% B,0.3% C, balance titanium was prepared by melting an electrode formedfrom compressed titanium sponge, pure aluminum wire, crystalline boronand pure graphite in a consumable electrode vacuum melting furnace. Theare voltage was 24 volts and the arc current 1400 a-mperes. The ingotwas processed to sheet as described in Example 3. This material had aYoungs modulus of 19.5 10* psi. a

We claim:

1. A quaternary alloy consisting essentially of, by weight, from 1 to 7%aluminum, 0.5 to 2% boron, 0.1 to 12% carbon andythe balance titanium,said alloy having a titanium-aluminum a solid solution matrix 'with theboron and carbon in the form of a precipitated dispersed phase withinsaid matrix.

2. A quaternary alloy consisting essentially of, by weight, from 3 to 7%aluminum, 0.5 to 2% boron, 0.1 to 1.2% carbon and the balance titanium,said .alloy having a titanium-aluminum 00 solid solution matrix with theboron and carbon in the form of a precipitated dispersed phase. withinsaid matrix.

3. A quarternary alloy consisting essentially of, by weight, about 5%aluminum, about 1.5% boron, about 0.3% carbon and the balance titanium,said alloy having a titanium-aluminum oz solid solution matrix with theboron and carbon in the form of a precipitated dispersed phase withinsaid matrix. 7 1

References Qited by the Examiner UNITED STATES PATENTS 2,818,333 12/57Swazy et al. 75-'175.5 2,892,742 6/59 Zwicker et al. 75'175.5 2,938,7895/ Jaifee 7=5-175.5

DAVID L. REOK, Primary Examiner.

1. A QUATERNARY ALLOY CONSISTING ESSENTIALLY OF, BY WEIGHT, FROM 1 TO 7%ALUMINUM, 0.5 TO 2% BORON, 0.1 TO 1.2% CARBON AND THE BALANCE TITANIUM,SAID ALLOY HAVING A TITANIUM-ALUMINUM A SOLID SOLUTION MATRIX WITH THEBORON AND CARBON IN THE FORM OF A PRECIPITATED DISPERSED PHASE WITHINSAID MATRIX.